Structural adhesives are typically thermosetting compositions that can be used to replace or augment conventional joining techniques such as screws, bolts, nails, staples, rivets, and metal fusion processes such as welding, brazing, and soldering. Structural adhesives are used in a variety of applications such as within the automotive and aerospace industries. To be useful as a structural adhesive, good mechanical strength and impact resistance are desired.
The physical properties of structural adhesive bonds depend on the interaction of the structural adhesive with the surface of the substrates to which the structural adhesive is applied. Under ideal conditions, the structural adhesive is applied to a clean surface; however, the surfaces of some substrates are contaminated with a hydrocarbon-containing material such as various oils and lubricants. Oil contamination is not uncommon on substrates that are part of a vehicle such as an automobile. The presence of the oil contamination can lead to undesirable bond failure at the adhesive/substrate interface.
Removing hydrocarbon-containing materials from the surfaces of substrates can be difficult. Mechanical processes such as dry wiping and/or using pressurized air tend to leave a thin layer of the hydrocarbon-containing material on the surfaces. Liquid cleaning compositions can be effective but these compositions typically need to be collected and recycled or discarded. Additionally, a drying step is typically needed after the cleaning step.